Heat erasable photosensitive coating and process of using same



United States Patent 3,169,064 HEAT ERASABLE PHQTOSENSITIVE COATING AND PRGCESS 0F USlNG SAME Marilyn Levy, Red Bank, N.J., assignor to the United dtates of America as represented by the Secretary of the Army No Drawing. Filed Nov. 5, 1963, Ser. No. 321,651 5 Claims. (Cl. 96-27) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

The invention relates to a novel photographic recording system wherein ultraviolet light is used to produce a print-out image upon a specially sensitive material. The material reacts to the application of heat to erase the printed image. The sensitive material may then be reexposed to provide another image. This procedure may be repeated many times.

The sensitive material may be in the form of a sheet or a coating on a suitable support and consists of a combination of phosphotungstic acid dissolved in polyvinyl butyral solution the composition of which will be specified hereinafter. This compound may be moulded into self supporting sheets or it may be given a consistency suitable for applying a coating upon a support.

In the practice of the invention the subject it is desired to reproduce may be a transparency of any type such as a photographic negative which is arranged for illumination by an ultraviolet light source. To print the subject it may be held in contact with the sensitive coated material while the light source is activated for the required time which may be about 1 second. The picture will then appear upon the sensitive element without further processing. The exposure may also be made by optical equipment such as a photographic enlarging device in which case the print may be made any required size.

The image thus produced will persist for a substantial period of time such as several hours in ambient room lighting during which period the image may be electronically scanned or copied by a conventional photographic procedure. When the image has served its purpose it may be erased by the application of heat which restores the sensitive surface to its original condition ready for another exposure.

It is a primary object of the invention to provide a photographic system suitable for performing a direct printing out dry reproduction operation in which a reusable sensitive printing medium provides a printed image in a minimum of time and wherein the printed image persists for a substantial period of time.

A further object of the invention is to provide a fast photo printing medium which produces a finished picture by mere exposure to the printing light.

A further object of the invention is to provide a printing system wherein the print material may be reused many times.

A further object of the invention is to provide a system wherein a print out image is produced which may readily be erased by the application of heat without damage to the printing material.

Other objects and features of the invention will more fully appear from the following description and will be particularly pointed out in the claims.

To provide a better understanding of the invention particular embodiments thereof will be described in detail.

Direct printing out photographic systems have been proposed which use phototropic compounds for their sensitive elements. One such system uses a sensitive coating consisting of phosphotungstic acid combined with hydroxyethyl cellulose or polyvinyl-pyrrolidone. This 3,169,064 Patented Feb. 9, 1965 compound has phototropic properties. However when an image is impressed thereon it automatically and gradually fades in the dark and is not affected by heat and consequently cannot be erased at Will.

'In the present invention the sensitive material is a combination. of phosphotungstic acid and polyvinyl butyral. This combination creates a sensitive coating material which produces a print out image without subsequent processing which persists for a substantial period and is unaffected by the presence of light. This image can be copied photographically or scanned electronically and then may be completely erased by applying heat thereto. The material then may be reexposed and erased many times.

A suitable example of such material is as follows.

Gms. Phosphotungstic acid 2 to 10 Polyvinyl butyal solution compounded as follows: polyvinyl butyral, 90 gms.; isopropyl alcohol, 510 gms.; ethyl alcohol, 200 gms. 10

This material may be coated on paper or other suitable material and may also be formed into a sheet or strip and used without a supporting device.

In using this material an exposure of the subject negative or other object to be photographed is arranged to impress a sharp image thereof upon the sensitive material by the application of light from an ultraviolet source. It has been found that an image is recorded in less than 1 second by a lamp of approximatelyv 140 watts placed about 5" from the subject. After the printing operation the image is utilized and then heat is applied to erase the image so that it may again be exposed.

Any suitable means may be used to apply the heat such as a combination electric heating unit and fan similar to the type used for drying hair, an infrared heat lamp or by a heating iron such as a tacking iron.

The composition of the sensitive material in the above example may be modified by the addition of small quantity of glycerine and sodium lauryl sulphate. The total weight of these added materials may be 2% to 5% of the total weight of the materials used in the example given.

The sensitive coating may be used in a different cycle of procedure for example it may be used as a heat sensitive material to make reproductions. In this use of the material the coating is given an all over exposure to ultraviolet light which produces a black surface. This black film is then exposed to a source of radiant heat or a stream of heated air while in contact with the subject. Wherever the sensitive material is exposed to the heat the dark surface becomes faded and thus reproduces the subject.

It should be noted that all operations in the system of the invention may be carried out in ordinary room light. An important application of the invention is in storing digital or other information in computing equipment where storage is for a short period. In this application an electrical signal originating at one point in such a system may be converted to a light image which image is used to expose the sensitive film of the invention.

The image thus formed can then be scanned with another plying the coating to a support to provide a printing element, exposing the coating to an ultraviolet image, utilizing the image thus printed upon the sensitive printing element and erasing the printed image by applying heat thereto.

2. A method according to claim 1 wherein the sensitive coating is composed of:

Gms. Phosphotungstic acid 2 to 10 Dissolved in the following so1ventpolyvinyl butyral, 90 gms.; isopropyl alcohol, 510 cc.; ethyl alcohol, 200 gms. 5 to 50 3. A method according to claim 1 and wherein the sensitive material has added thereto a small quantity of glycerine and sodium lauryl sulphate constituting about 2% to 5% by Weight of the materials in the sensitive coating.

4. A method for photographically recording comprising preparing a direct printing out photosensitive coating containing phosphotungstic acid and polyvinyl butyral, applying the coating to a support to provide a printing element, converting an electrical signal into an ultraviolet light signal, exposing said coating to said ultraviolet signal, storing the resulting ultraviolet image, subsequently scanning the ultraviolet image with visible light, utilizing the image derived from scanning and erasing the ultraviolet image by application of heat thereto thereby clearing the printing element for subsequent recording operations.

5. A photosensitive material comprising the following ingredients compounded in the proportions indicated:

Grains Phosphotungstic acid 2 to 10 Dissolved in the following solvent-polyvinyl butyral, 90 gms; isopropyl alcohol, 510 gms; ethyl alcohol, 200 grns. 5 to 50 References Cited by the Examiner UNITED STATES PATENTS 2,709,134 5/55 Jacobs et al.

2 2,723,914 11/55 Suchow.

3,085,469 4/63 Carlson.

NORMAN G. TORCHIN, Primary Examiner. 

1. A METHOD FOR PHOTOGRAPHIC RECORDING COMPRISING PREPARING A DIRECT PRINTING OUT PHOTOSENSITIVE COATING CONTAINING PHOSPHOTUNGSTIC ACID AND POLYVINYL BUTYRAL, APPLYING THE COATING TO SUPPORT TO PROVIDE A PRINTING ELEMENT, EXPOSING THE COATING TO AN ULTRAVIOLET IMAGE, UTILIZING THE IMAGE THUS PRINTED UPON THE SENSITIVE PRINTING ELEMENT AND ERASING THE PRINTED IMAGE BY APPLYING HEAT THERETO. 